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80 Cards in this Set
- Front
- Back
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how do xrays and gamma rays differ?
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x rays originate from outside of the nucleus and generate high speed particles. Gamma rays originate from the inside of the nucleus and form spontaneously decaying atoms.
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what are the basic components of an x ray tube?
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Glass tube: vacuum environment to prevent incidental interaction of the electron beam with air. Electron beam: travels from negative cathode towards positive anode
Cathode: has filament and focusing cup and is low voltage. Filament: dense source of electrons, has high melting point. Focuising cup: around the filament to keep the electron cloud from dispersing. The low voltage of the cathoe is across the filament to force current through the resistance of the filament. Causes release of free electrons as a cloud around the filament- thermionic emission. The anode has target and focal spot and is high voltage. The target: the electron beam is aimed at the target. A steeper target angle gives a smaller effective focal spot. The focal spot is an area on the target at white the interaction of high speed particles takes place. The high voltage of the anode across the tube accelerates the electrons from the filament towards the target. |
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What are the limits of production of xrays in an xray tube?
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The amount of heat from the filament, amount of interactions that result in em radiaion, and the amount of em radiation that is in the xray energy range. HEAT PRODUCTION AND DISSIPATION IS THE MAJOR LIMITING FACTOR IN X RAY PRODUCTION.
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What are the differences between stationary and rotating anode xray tubes?
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Stationary: all electrons aimed at a fixed area.
Rotating: electrons are aimed at the edge of a rotating disc so heat production is spread over a larger surface area |
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Advantages and disadvantages of stationary vs rotating anode tubes?
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stationary: more portable, less heat dissipation so less xray output.
Rotating: more heat dissipation and more xray output. More complex and expensive. Most rotating have 2 filaments so either a small or large focal spot can be generated. Larger filament because the larger focal spot allows for decreased exposure time and decreased motion |
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what is kvp?
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kilovolt peak. The potential difference causing electrons to flow between cathode and anode. measured by voltage.
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what is mas?
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filament current (mA) and the exposure time (S)
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How are xray beams characterized?
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quality: energy of the xrays within the beam, higher energy x rays can penetrate thicker objects.
Quantity: number of xrays in a beam |
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What controls the characteristics of an x ray beam and how?
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quality: KvP
quantity: mas and KvP kvp determines the energy of the electrons in a beam (# of interactions per electron accelerated) by controlling the potential difference across the tube. ma determines the rate of electron emission by forcing more or less thru the filament. s determines the length of time that electrons flow from cathode to anode. Hugher mas increases the number of electrons in the beam (quantitY0 by increasing the amount of current or by increasing the time that they flow. |
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what are xray filters?
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Selectively remove low energy xrays from the primary beam. Inherent: glass tube and lead housing. Added: sheet of aluminum or copper thats placed between the xray tube and collimater. Low energy xrays get absorbed by the patient so filtering the lows means less exposure to the patient
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what are collimators?
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adjust the size of the xray field. Absorb unnecessary portions of the primary beam. increases image quality by decreasing scatter radiation.
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what are gris?
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plates made up of alternating thin lead and al strips that reduce the amount of scatter radiaiton striking the film
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what is film fog?
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overall grayness of a film due to scatter radiation
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what are focsed grids?
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match the angle of divergence of the primary beam. use 2-3x mas when using a grid
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what is compton scattering?
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primary xray photon strikes atoms in the patient, producing low energy seconary x ray photons which strike the film at random angles. Scatter rad increases with tissue density and kvp so grids used for thick or high density tissues or large field
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what is the grid ratio?
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ratio between hight or lead strips and distance between them. higher frid ratios remove more scatter radiation and primary xrays so have to use higher mas.
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What is a bucky tray?
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noisy. moves grids back and forth (perpendicular to lead strips) to blur grid lines. When exposed with a stationary grid, see lines
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what is lateral decentering:
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grid artifact that occurs when the grid isnt centered to the xray tube. General underexposure
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what is angled frid?
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grid artifact that occurs when the grid is at an angle raltive to the xray beam. causes severe general underszposure and lots o grid lines
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what happens with an upside down grid?
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causes white out (complete unerexposure) of film edges
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What is in the film/
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silver halide crystals in goo. Single emulsion is on one side - ultrasound film. double emulsion: rad film.
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how does xray film work?
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silver halide absorbs the xray and emits a photoelectron. the photoelectron is caught by a sensitivity speck in a crystal which attracts silver ions. the entire crystal is converted to metallic silver in development
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If you use green sensitive film, what type of light should you use?
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red safe ligh
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what is an intensifying screen?
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light emmitting crystals in a plastic support. Allow a reduction in the number of xrays required to expose the film. X rays ooming from the patient are absorbed by phosphors of the screen. They spit out a breif burst of ligt and the light exposes the screen betwen the two intensifying screens in the cassette.
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What is the difference between fast and fine (detail) intensifying screens?
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Fast: thick phosphor layers and big crystals decrease detail but allow shorter exposure time which decreases motion artiffacts. LA. Fine (detail) screens: thin phosphor layer and small crystals increas sharpness but you need a higher mas
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what affects the type of film that must be used?
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the color of light emitted by phosphors on the intensifying screens
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What is a screen craze?
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Intensifying screen artifact. occurs when theres cracks in the screen emulsion. Sharp marginated white dots or lines
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What are the properties of a cassette?
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front is radiolucent (al or carbon filter) and back is lead foil to absorb backscatter.
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What is the max allowable exposure inrem?
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5 rem/year: whole body
500 mrem for pregnancy duration 50 rem skin of hands/feet 6000 rem is fatal |
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what is the most important source of natural radiaion?
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radon
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what are 3 ways to protect yourself from exposure?
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limit time, increase distance and use sheilding
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What factors detract from an accurate radiographic image?
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magnification, distortion and unsharpness
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what determines the size of the projected image of an object?
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sfd and tfd
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how is magnification minimized?
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minimize sfd and max tfd
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to what does geometric distortion refer
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the misrepresentation of the subject relative to size, shape and position
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penumbra?
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partial shadow on the edge of the actual image. results in unsharpness or blurrin
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what causes penumbra?
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caused by definition/projection of the edge of an object by x rays coming from different angles
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how do magnification and penumbra relate to affect image detail?
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magnification enlarges penumbra which owuld decrease image detail
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what is the single greates deterrent to imgae unsharpness?
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motion
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is it better to use a small ro large focal spot?
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smaller focal spot since they generate smaller penumbra and less magnification. Also means a smaller ma which would increase your exposure time and incidence of motion artifacts
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relate distance and intesnsity of the xray beam
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inverse square law: intensity of the beam is directly porportional to the mas and inversely proportional to the square of the distance. the farther the distance from the source, the lower the intensity of the beam
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what is the heel effect?
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uneven intensity of the xray beam within the ield. x ray beam has greater intensity on the cathode side and lss on the anode siede because absorption of a portion of the xray beam by the target itself leads to xrays produced deeped in the target must transgerse a greater distance to escpae. heel effect is influence by the angle of the target and field size. thicker end of patient near cathode end
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What factors do objects in the xray beam alter the beam emerging from the patient?
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intensity of the bem as it emerges is directly proportional to the originial intensity of the beam and inversely proportional to the thickness of the object and absorption coefficient of the tissue. the more intense the beam entering = the more intense exiting. thicker the patient, less that will exit.
mas, kvp, cm, mu |
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list the radiographic tissue densities in order or INCREASING radiopacity
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air < fat<water< bone< metal
All Fat Women Beat Men |
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Describe the differences in the radiographic apperance of water, blood, transudates and exudates
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white areaas mean that there are less xrays getting throu and therefore more dense object. Higer attenuation coefficeint. Air: more xrays passing thru with higher intesntiy. soft tissue: made of water. all soft tissues look gray. free fluids: cant be differentiated
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explain the summation effect
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radiographic densicites or opacities are additive
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2 examples of the summation effect
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superimosed cranial and caudal poles of kidneys. low density objects like lymph nodes appear as shadows
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summation effect in abnormal pt
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tumore in chest superimposed on heart, mass on muscles
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silhoette effect
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margins of objects of same tissue density that are in contact cant be differentiated
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2 examples of the silhouette effect in normal pt
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vasculature in muscle, urine in bladder
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2 exapmles of silhouette effect in abynormal pt
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fluid filled abdomen has uniform appearnce. lung with alveolar disease same density as heart
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what is required ffor visualization of an air-fluid interface?
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horizontally directed beam. air will rise to the top
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list of radiographic signs
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density: inherent tissue density. increased = mineralization, decreased - soft tissue with gas, bone with osteolysis
geometry: size, shape, number, position, margination function: need special procedures. integrity, patency, motility, excretion |
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describe how lateral or vd should be viewed.
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lat: both r and l views as r laterals (head at your left. VD: as vds with the pts right side to your left
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what are the legal requirements for labeling?
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permanent, applied before development, owner of the rad, date and patient id
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how does a photoprinter work?
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cassette has blocker. use light source to imprint
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what factors affect rad contrast
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subject contrast: nherent in the tissues (thickness, atomic #, density) can reduce the inherent subject contrast by increasing kvp and decreing mas.
fog: light exposure, safelight mismatch, pressure, static. |
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explain film processing
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developing: softens the emulsion and converts exposed, unionzixed silver halide crystals to metallic silver.
Fixing: remove unexposed silber halide rinsing: remove chemical and harden dry: final hardening |
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technique chart:
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predetermined settings. be consistant, use thickest part, keep exposre time less than 1/30, increase kvp for fatness. decrease for skinnies
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list the common radiographic artifacts:
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too long deveop or too high temp: too black (too much silver halide turns).
Bad mix of developer: incomplete blackening bad fixer: chalky green dichroic stain. bad rinse: sticky too close: kissing artifact too hot drying: cracks |
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how does negative contrast media alter the image
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lesser radiopacity than normal tissues. low density with little attenution of xrays. fill with gas, improve visual of structures
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how does postive contrast alter the image
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greater radiopacity. high attenuation coefficient.
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what are the 2 main classes of positive contrast media?
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barium and iodine
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procedures that use negative contrast
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pneumocystography, pneumocolon, pneumo blah
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examples that use positive contrast
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intraluminal or intracavity. alimentary, angiography, cystography, etc
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what factors determine which contrast should be used?
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organd to be studeied and suspecte abnormality
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what is the greatest composition of ionic urographic and angiographic contrast media?
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water soluble, tri iodinated, benzoic acid derivatives. aquesous, organic iodinated cm
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what is the general composition of non-ionic urographic and angiographic contrast media?
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glucose derivatives with many I atoms- not benzoic acid, less hypertonic
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which contrast media use for esophagram?
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BaSO4 paste
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what CM use for upper gi?
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BaSO4 liquid
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what cm to use for lower gi?
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BaSO4 liquid
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what CMI to use for urographic and angiographic?
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organic iodinated CM
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give an example of an urographic contrast medium
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sodium iothalomate or methylglucamine diatrizoate
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why would one use an aq organic iodinated cm for routing use in gi studies?
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suspected alimentary tract perforation
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how do myelographic CM differe?
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iohexol and iopimadol- non ionic CM with lower osmoality and fewer side effects
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What is digital radiography
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uses x ray energy and computers. digital reord
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how are images formed with digital rad (indirect)?
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use casette and light sensitive phospher screen. scan plate.
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how are images fromed with digital rad (direct)?
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amophous selenium in flat panal to convert absorbed xray into liberated es
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advantages of high versus low frequency transducers:
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higher = better resolution but lower frequncy. use highest frequency that allows for best penetration
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when does reflection occur
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between tissues that differ in acoustic impedence (the speed of sound in a tussue times the density). grater the difference = greater reflection
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